Towards Economically Feasible Recycling of Spent LiFePO₄ Black Mass: A Thermodynamic-Assisted Targeted Delithiation Strategy

Abstract

The recycling of spent LiFePO4 batteries is hindered by economic inefficiencies, primarily due to poor selectivity during lithium recovery. Here, we present a thermodynamic-assisted electrochemical delithiation strategy to achieve highpurity lithium extraction. By refining thermodynamic models of the Li-Fe-P-H2O system, we delineate a precise operational window (pH 4.0-5.2, oxidation potential 0.15-0.4 V) that favors Li + extraction while stabilizing the FePO4 framework, as verified by in-situ electrochemical quartz crystal microbalance. Crucially, we reveal that trace yet persistent iron dissolution originates from a proton-coupled reaction forming an unstable HFePO4 intermediate, a previously overlooked mechanism that redefines the stability limits of the material in aqueous media. This work establishes a targeted, energy-efficient recycling pathway and provides fundamental insights into ion-exchange dynamics in olivine-type cathodes.